1. Field of Invention
The invention generally relates to systems and methods for mounting various devices, which mounting systems and methods provide at least one axis of rotation about which rotational motion is damped. More particularly, the invention relates to mounts that provide active electronically controlled damping via electric motors.
2. Description of Related Art
In military strategy, there is a great desire to be able to view the enemy so as to allow an offensive military force to bring weapons to bear on the enemy while maintaining certain protections for the offensive force. Some protection can be provided by maintaining distance from the enemy. One method used to bring fire down upon an enemy from a distance is the artillery barrage. Artillery weapons are generally designed to have an extremely long range and are capable of firing at targets to which there is no direct line of sight from the weapon (e.g., due to intervening terrain) by firing their ordnance in high arcs. This capability provides another level of protection in that these weapons can be usefully located in positions where they are hidden, such as by the terrain. Artillery batteries are often safe from fire from the enemy, as the enemy cannot locate them to direct retaliatory fire. Even if the enemy knows their location, the enemy may not have access to weapons with sufficient range to reach them.
The problem with firing artillery, however, is that the ordnance fired must somehow be aimed so that it is accurately delivered onto enemy positions, instead of being fired randomly or, worse, fired upon friendly positions which may be nearby. Since the artillery batteries generally cannot sight the enemy directly, they often rely on forward observers to locate targets, and to provide updates on these positions so the artillery battery can track the targets and adjust their aim appropriately.
Traditionally, forward observers were infantrymen who moved to positions within sight of the enemy. Using a remote communications method such as radio, forward observers instructed the artillery gunners where to fire in order to hit targets relative to the forward observer's own location. As visual enhancement technologies became more sophisticated, machines began to be used to enhance human visual capabilities, including range of sight. These machines range from a simple pair of binoculars to advanced night vision and RADAR systems. As the technology has advanced, the bulk and weight of these machines has increased. Therefore, in much of artillery sighting today, a vehicle is used to carry a sensor suite of various vision enhancing machines. The vehicle also carries a crew of a few individuals who, by using the sensor suite and other on-board technology, locate enemy targets and return those locations to the artillery batteries. Generally, in the U.S. Army these personnel are members of the Combat Observation Lasing Team (COLT), the mission of COLT being to act as the mobile forward observer for the artillery. While a targeting sensor suite may be mounted on numerous vehicles, for simplification (but not be way of limitation of any disclosure herein) the vehicle on which a sensor suite as above discussed is mounted will be referred to as a COLT vehicle.
On board the COLT vehicle is a sensor suite for use in targeting that often comprises an infrared camera for night operations, day view optical telescope, a laser rangefinder, a laser target designator for laser guided weapons, and an Inertial Navigation System (INS), or other similar devices. This sensor suite is usually attached to a ring mount on the roof of the vehicle carrying the sensor suite, which ring mount can rotate through 360°. On the COLT vehicle, along with the sensor suite, there is also generally a Mission Processor Unit (MPU) and a communications computer, which are used to link into the tactical radio network allowing targeting information from the sensor suite of the COLT to be transmitted to units or weapons in the artillery battery for use in aiming long range weapons. The sensors in the sensor suite are accurately aligned to one another and to the INS so that the errors are usually extremely small and targeting accuracy is high when targets are acquired and accurately tracked by the sensor suite.
In order to allow the sensor suite to target the enemy, particularly when the enemy is on the move, the sensor suite will generally be supported on a mount which is often a gimbal-type mount called a Traversing Unit (“TU”), which is in turn mounted to the ring mount on the roof of the vehicle. The TU allows the sensor suite to be moved in azimuthal and attitudinal (also referred to herein as elevational) angles, providing the sensor suite with the capability to track targets moving in any direction.
The sensors typically have high magnification to allow observing and targeting at great distances (generally miles). This high magnification can make the tasks of acquiring and accurately tracking targets difficult when manually performed. As opposed to computer controlled systems where remote control can utilize small motors and gearing to execute very small directional changes, in a human-powered (manually controlled) system, which are preferred in some circumstances, particularly due to issues of weight, cost, and simplicity of manufacture and operation, the application of force by human muscles is used to direct movement of the TU. The human body, however, is fairly imprecise when it comes to small movements. Human musculature is designed for fairly large movements. Because of the sensitivity of the sensor suite and the accuracy required to effectively target the artillery batteries, the TU needs to be designed to reduce vibration and other unintended motions caused by the imperfections of the human user. As is well known, due to the great distance over which targeting occurs, a small rotation of the sensor suite by only tens of microradians can lead to deviations of many meters in the calculated location of the target.
For these reasons, rotation of the TU in both the azimuth and elevation axes is preferably damped to provide a resistive torque to make sensor movement controlled and smooth. By providing a damping torque, the effects of small unintended torque inputs by the user are minimized. Damping provides the system with a “feel” translated to the user to assist their motion in being smooth and provide for a more uniform movement allowing the human user to rotate the sensor suite more accurately, and at lower rates. The TU also preferably includes a “slip clutch” effect to limit the damping effect at high rotational speed so that the sensor suite can be spun around to acquire targets in a different sector quickly and without having to fight increased resistance. Further, the amount of resistance preferably increases the faster the device is being moved.
Currently, TU systems utilize fluid resistance to create the damping effect. One such fluid damping system is described in U.S. Pat. No. 3,885,453, the entire disclosure of which is herein incorporated by reference, for the targeting of a missile launcher. Fluid damping systems also generally include a slip clutch to allow for high speed movement for additional target acquisition. The TU damping and clutch system is tuned with fluid orifices and springs to get a system balanced for the weight and inertia of the sensor suite, the capabilities of the operator, and the capabilities of the sensors. This tuning tries to match the system to the mission, and soldiers are trained to use the system and the profile of the system to target accurately.
FIG. 1 provides for an embodiment of the resistance profile (also termed a damping function or a damping torque curve) of fluid damped systems under testing conditions and for manually acquiring a target and for tracking moving targets at distances between 1000 and 5000 meters. The fluid damped systems also include a slip clutch allowing the sensor to be rotated at speeds above 3°/sec without increased resistance above that provided at 3°/sec, which allows the operator to specifically re-acquire targets in other sectors. As can be seen in FIG. 1, there are significant changes in the resistance profile depending on the rate of rotation and the ambient temperature. For instance, the line 101 represents a target resistance profile for which the resistive torque increases exponentially as the slew rate of the sensor suite increases up to a designated slew rate. At a fixed point 103, the slew rate is determined to be a rapid traverse move, and the slip clutch is activated, fixing the resistive torque at a level value (as shown by the leveling of line 101). The wide block (cross-hatched) line 105, showing variance on either side of line 101, represents the tolerance of fluid damped systems at a fixed temperature (77° F.). The variation about the target line 101 is a result of the variation in the behavior of the fluid damping assemblies due to such factors as the exact viscosity of the fluid used, calibration of components, and accuracy in machining and machine tolerances. Small variations in design can result in relatively dramatic changes.
Also visible in FIG. 1 are two curves 107 and 109 that show variations for high temperature, 145° F. (curve 107), and low temperature, −25° F. (curve 109), for a single fluid damping assembly. These expanded limits exist because of the wide variation in the fluid viscosity as a function of temperature. Colder fluids generally become more viscous, while hot fluids are generally less viscous. Therefore, even if the system has a known resistance curve at a first temperature, changes in the temperature can alter the curve as the temperature changes. The net result is that the TU damping characteristics vary as much as 15 ft-lb over the temperature range shown resulting in variable performance in the target acquisition and tracking tasks.
This difference in performance makes it difficult for the human user to accurately target in different conditions as the TU's “feel” (that is the amount of force they must generate to carry out a particular movement) will change depending on environment, and even across relatively identical units. Further, this change may necessitate constant recalibration and user practice with the TU to make sure that the human operator can use the unit effectively as they must constantly adjust to slight variations. For this reason, it is preferable that a TU provide consistent damping characteristics from unit to unit and across its operational temperature range. Clearly, as shown in FIG. 1, existing TUs utilizing fluid damping result in wide damping variations and fall woefully short of consistency, leading to difficulty in their use and inaccuracy.